This application is based on Japanese Patent Application 2000-169482, filed on Jun. 6, 2000, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device with bumps for pads.
b) Description of the Related Art
FIG. 6 is a cross sectional view showing a conventional semiconductor device having an electrode pad and a bump formed over the pad.
An interlayer insulating film 100 is formed on a semiconductor substrate. An electrode pad 101 is formed on a partial upper surface of the interlayer insulating film 100. A protective film 102 covers the surfaces of the electrode pad 101 and interlayer insulating film 100, the protective film 102 having a two-layer structure of a silicon nitride film and a silicon oxide film. An opening 102a is formed through the protective film 102 to expose a partial upper surface of the electrode pad 101.
An insulating film 103 of polyimide is formed on the electrode pad 101 and nearby protective film 102. An opening 103a is formed through the insulating film 103 to expose a partial upper surface of the electrode pad 101. The inner surface of the opening 103a and the upper surface of the insulating film 103 near the opening 103a are covered with a three-layer lamination of a Ti film 105, a Cu film 106 and a Ni film 107. A solder bump 108 is formed on the Ni film 107.
The Ti film 106 promotes adhesion to the Cu film 106. The Cu film 106 promotes adhesion to the Ni film 107. The Ni film 107 prevents constituent elements of the solder bump 108 from diffusing into the electrode pad 101.
The solder bump 108 covers not only the upper surface of the Ni film 107 but also the side wall of the lamination from the Cu film 106 to Ni film 107. Tin (Sn) atoms in the melted solder bump 108 diffuse into the Cu film 106 from its side wall. The region where the Sn atoms were diffused expands its volume so that the Cu film 106 is susceptible to peel-off.
If the Cu film 106 is peeled off, solder enters a gap formed at the interface between the Ti film 105 and Cu film 106. Sn atoms in the solder entered the gap further diffuse into the Cu film 106. Peel-off progresses still more inward. As the peel-off progresses, adhesion of the bump is degraded. If Sn atoms reach the electrode pad 101, the electric characteristics such as a wiring resistance are deteriorated.
It is an object of the present invention to provide a semiconductor device capable of suppressing adhesion reduction of a bump and an increase in resistance of a wiring connected to the bump.
According to one aspect of the present invention, there is provided a semiconductor device comprising: a conductive electrode pad formed on a partial area of an insulating surface; an insulating film covering the electrode pad, the insulating film having an opening exposing at least a partial upper surface of the electrode pad; a barrier layer of conductive material formed on the partial upper surface exposed on a bottom of the opening and on a surface of the insulating film near the opening; and a conductive bump adhered to the barrier layer, wherein a step is formed on a surface of a layer under the barrier layer between an outer periphery of the barrier layer and an outer periphery of the opening.
The step prevents a further progress of a gradual peel-off of the barrier layer from its outer periphery. It is therefore possible to suppress the peel-off of the barrier layer and improve adhesion of the bump.